A high idle speed can be caused by a poor connection at the Throttle Position Sensor (TPS). Connector replacement kits are available from Mazda dealers and possibly some Ford dealers.
Car Problem Reports
Mazda B2500 High Engine Idle with Manual Transmission
Mazda B2500 Problem
Engine Affected: 2.5L 4 Cylinder
Average Mileage: 113,250 mi (61,000 mi - 170,000 mi)
Visitor, 1998 Mazda B2500, 2.5L 4 Cylinder, 97,500 mi
when I'm driving along. I put the trans in nutural to stop so I don't have to use the clutch.Thats when the motor starts ideling fast.It goes to about 4000 rpm's before it goes back to where it belongs just under a 1000 rpm's. I think it could be a vacume leak? I'm not sure...
Visitor, 1998 Mazda B2500, 2.5L 4 Cylinder
Idle surges to high rpm's? Idle sensor connector at top middle rear of motor gets dust in it. Disconnect, blow out, and tape w/electrical tape to keep dust out. Never had a problem since.
Visitor, 2000 Mazda B2500, 2.5L 4 Cylinder, 114,000 mi
I have a 2000 B2500, with the manual transmission. I had the high idle problem and the poor idle condition. Every once in a while it would run rough and no engine light. I replaced the throttle position sensor,and took apart all the harness connection spots and cleaned them. I also replaced the timing belt, water pump, spark plugs, and the wires. The truck runs perfect now. I don't know witch one of those fixed that problem, but for about 200 dollars in parts and a weekend of working on it, it runs perfect. I get about 2-3 more miles per gallon now also. Its well worth the time to just replace everything listed above and be done with it.
Visitor, 1999 Mazda B2500, 2.5L 4 Cylinder, 61,000 mi
Engine speed increases, often as high as 3500 rpm, when clutch is depressed. Doesn't happen all the time. Drops back to normal when truck is brought to a stop.
Visitor, 2000 Mazda B2500, 2.5L 4 Cylinder, 170,000 mi
I have had this 3 times (fixed twice) and only seems to happen when it is very hot outside.